1590s, "born out of wedlock," from Latin spurius "illegitimate, false" (source also of Italian spurio, Spanish espurio), from spurius (n.) "illegitimate child," probably from Etruscan spural "public." Sense of "having an irregular origin, not properly constituted" is from c.1600; that of "false, sham" is from 1610s; of writing, etc., "not proceeding from the source pretended, 1620s. Related: Spuriously; spuriousness.